Azeotropic composition

ABSTRACT

THE DISCLOSURE ALSO RELATES TO TERNARY AZEOTROPES OF TETRACHLORODIFLUOROETHANE AND TRICHLOROETHYLENE WITH ISOPROPANOL.

United States Patent 3,554,918 AZEOTROPIC COMPOSITION John Allan Schofield, Irvington, and Roger A. Delano,

Dobbs Ferry, N.Y., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Oct. 24, 1967, Ser. No. 677,715 Int. Cl. C09d 9/00; Clld 7/50; C23g /02 US. Cl. 252171 1 Claim ABSTRACT OF THE DISCLOSURE The disclosure also relates to ternary azeotropes of tetrachlorodifluoroethane and trichloroethylene with isopropanol.

This invention relates to an azeotropic composition and particularly to the binary and ternary azeotropic mixture of tetrachlorodifiuoroethane and methanol or any one of the isomers, n-butanol or iso-butanol of sec.- butanol. The present invention also relates to ternary azeotropes of tetrachlorodifluoroethane and trichloroethylene with either methanol or ethanol or isopropanol. In a further embodiment ternary azeotropes have been discovered comprising tetrachlorodifluoroethane, trichloroethane and either methanol or ethanol or isopropanol.

Several of the chlorofiuoroethanes have attained widespread use as specialty solvents in recent years, particularly tetrachlorofluoroethant. This is a relatively high melting compound (CCl FCCl F, 24.5 C.), which is nontoxic and nonflammable, and which has satisfactory solvent power for greases, oils, waxes and the like under certain conditions. It has therefore found use in cleaning electric motors, compressors, lithographic plates, typewriters, instruments, gauges, and as non-corrosive brines.

For certain solvent purposes however, the chlorofluoroethanes alone have insufficient solvent power. This is particularly true in the electronic industry during the manufacture of printed circuits. Printed circuits are well known in the electronics art; and consist of a circuit formed from a soft metal on a solid, non-conducting surface such as a reinforced phenolic resin. During manufacture, the solid surface is coated with the metal, the desired portion of metal is coated with an impervious coating, and the excess metal is removed by etching with a suitable acid. After the excess metal has been removed, it is necessary to remove the impervious coating because solder joints must be made to the printed circuit and these will not form if the coating is present. After the impervious coating is removed, the circuits are coated with a rosin flux to permit the joints to be soldered, after which the rosin flux must then be removed.

The chlorofiuoroethane solvent does not have sufficient solvent power to clean printed circuits; that is, to effectively remove the rosin flux. Although mixtures of solvents may be used for this purpose they have the disadvantage that they boil over a range of temperatures and consequently undergo fractionation in vapor degreasing or ultrasonic applications which are open to the atmosphere. When employing either of these cleaning or degreasing methods the solvent must also be both relatively nontoxic and nonflammable for safety reasons.

Tetrachlorodifluoroethane is a relatively high boiling fluorocarbon and for this reason is especially advantageous in vapor degreasing applications since at these temperatures the hot vapor has more of a tendency to dissolve high melting greases, or fluxes as well as oil residues and the like. When articles such as circuit boards are passed through a vapor degreaser, the solvent vapors tend to condense on the article until the articles are heated by the vapors from room temperature up to the temperature of the vapor. The condensation thus formed 3,554,918 Patented Jan. 12, 1971 ice on the articles tends to drip back into the solvent reservoir taking with it some of the soil on the article. For this reason the ability of a cleaning solvent to condense on the surface is especially advantageous. Higher boiling solvents prolong this condensation effect in a continuous degreaser since it takes a greater amount of time to bring the article passing through the degreaser up to the vapor temperature of the solvent. Consequently higher boiling solvents generally have better cleaning power per unit of time in a continuous vapor degreaser than the lower boiling solvents.

Tetrachlorodifluoroethane also is a better solvent than materials such as trichlorotrifluoromethane, however, it suffers the disadvantage that it is solidus at room temperature whereas the latter is liquidus. Accordingly tetrachlorodifluoroethane is more diflicult to handle than liquid type cleaning solvents.

It is an object of this invention to provide a constant boiling or azeotropic solvent that is a liquid at room temperature, will not fractionate and also has the foregoing advantages. Another object is to provide an azeotropic composition which is valuable as a solvent and particularly for cleaning printed circuits. A further object is to provide an azeotropic composition which is both relatively nontoxic and nonflammable both in the liquid phase and in the vapor phase and which at the same time is an excellent solvent for cleaning printed circuits especially by means of a continuous vapor degreasing machine.

The above object of this invention may be accomplished by a novel binary azeotropic composition of tetrachlorodifiuoroethane (e.g. 1,1,2,2-tetrachloro-1,2-difluoroethane) and either methanol or n-butanol or secondary butanol or iso-butanol; ternary azeotropes of tetrachlorodifluoroethane (e.g., 1,1,2,2-tetrachloro-1,2-difluoroethane) trichloroethylene and either methanol or ethanol or isopropanol; and ternary azeotropes of tetrachlorodifiuoroethane (e.g. 1,1,2,2-tetrachloro 1,Z-difluoroethane), trichloroethane (e.g. 1,1,1-trichloroethane) and either methanol or ethanol or isopropanol. Although 1,1,2,2-tetrachloro-1,Z-difluoroethane is a preferred tetrachlorodifluoroethane, the isomer, 1,l,1,2-tetrachloro-2,2- difluoroethane may be substituted therefore in whole or in part and especially in minor amounts or trace amounts. The preferred trichloroethane comprises the 1,1,1-trichloroethane isomer. All of these mixtures form azeotropes which distill at a constant temperature, the liquid phase and the vapor phase in equilibrium therewith having the same composition. Such mixture is relatively nonflammable and nontoxic in both the liquid phase and the vapor phase. These mixtures are particularly. useful as solvents for greases, oils, waxes, and the like and cleaning electric motors, compressors, lithographic plates, typewriters, precision instruments, gauges, and the like and are particular useful for cleaning printed circuits.

Although the azeotropic mixtures are obtained at approximately 760 mm. Hg a variation in pressure and consequently a change in the compositions and boiling points are also intended to be within the broad scope of the invention. Thus the azeotropes may contain many different proportions of all of the aforementioned components provided a constant boiling mixture is obtained at the various pressures at which the compositions are used. Stated otherwise any pressure may be employed to obtain the azeotropes of this invention as long as a three com ponent or two component constant boiling mixture is obtained, and accordingly the ratio of components of the azeotropes of the invention will also vary. The variation of components is thus within the skill of the art and is easily determined once it is known that the halogenated hydrocarbons of this invention will form the aforementioned azeotropes. In a preferred embodiment the present invention relates to the aforementioned azeotropes that boil at atmospheric pressure i about 25, especially 1 about 15 mm. Hg.

EXAMPLE I Composition Boiling point,

percent by F. 760 mm.

Components weight Hg 1,1,2,2-tetraehloro-l,2-dilluoroetltane 69. 3 140 Methanol 30. 7

EXAMPLES IIX The method of Example I is repeated using different mixtures of alcohols and/or 1,1,1-trichloroethane or trichloroethylene and 1,1,2,2-tetrachloro-1,2-difluoroethane, the results of which are as follows:

ing to the circuit. The board is then passed over a molten solder bath, contacting the desired joints with the molten metal, whereby the soldering is effected. After cooling, the excess rosin flux remaining on the board must be removed since, if present in the final assemly, it will lead to corrosion, poor electrical resistance and other deleterious properties.

The board is cleaned by placing it in an ultrasonic bath of any of the aforementioned azeotropes and operating at about 32 kilocycles per second at about 1020 F. belowtheboiling point of the particular azeotrope for about one minute.

When the board is cleaned with the azeotropic mixtures of this invention substantially all of the rosin flux is removed without any detrimental eifect on the board which constitutes the backing of the printed circuit.

Although the invention has been described by reference to some preferred embodiments it is not intended that the broad scope of the novel azeotropic compositions be limited thereby but that certain modifications are intended to be included within the spirit and broad scope of the following claim.

What is claimed is:

1. An azeotropic mixture consisting essentially of about 24.3 parts 1,1,2,2-tetrachloro-1,2-di-fluorocthane,

Components, percent by weight 1,1,1- 1,1,2,2-tetrai- Tritri- Boiling chloro-LZ-di- Metha Ironisehloloehloropoint, Mm. Hg fluoroethane nel Ethanol panol I3 utanol Butauol Butauol ethylene ethane F. pressure Exam 10 No.:

Printed circuit boards are usually prepared by impregnating glass cloth, nylon, or paper laminates with a phenolformaldehyde resin or an epoxy resin. Printed circuits are prepared by a variety of methods. In a typical procedure, the board consists originally of a phenolic resin impregnated base to which is bonded a sheet of copper, 2 to 4 mils thick, covering one surface of the board, The desired circuit is drawn on the copper with an asphalt based ink using the silk screen method. The

excess copper is then removed by etching with a ferric about 30.9 parts i-propanol and about 44.8 parts trichloroethylene on a weight basis.

References Cited UNITED STATES PATENTS 11/1966 Hirsch et al. 252171 OTHER REFERENCES Mellan: Industrial Solvents, Reinhold Publ. Co. (1950) page 75.

Handbook of Chem. & Physics (48 ed.) The Chem. Rubber Co. (1967') page D21.

LEON D. ROSDOL, Primary Examiner W. E. SCHULZ, Assistant Examiner U.S. Cl. X.R. 

